The present invention relates to a submerged membrane bioreactor, and particularly to a non-woven fabric membrane filtration module disposed therein.
In an activated sludge process for treating wastewater, the use of an ultrafiltration (UF) or microfiltration (MF) unit in a solid/liquid separation membrane bioreactor to replace the sedimentation tank/sand filtration tank started in 1969. In comparison with the conventional activated sludge process, the solid/liquid separation membrane biological treatment technique has many technical advantages, e.g. a long sludge retention time, capable of treating wastewater with a high concentration variation, without the need of using a sedimentation unit (less footprint), etc. Up to now, there are at least 500 solid/liquid separation membrane biological treatment plants being operated world-widely. Most of the membrane materials used by the plants are microporous polymeric materials (with a pore size of 0.1xcx9c10 xcexcm) or inorganic ceramic materials. Typical examples include U.S. Pat. No. 5,204,001, which discloses a membrane bioreactor system for treating wastewater from a metal processing plant; and WO0037369, which discloses a membrane bioreactor for nitrogen-containing water treatment.
U.S. Pat. No. 5,772,821 discloses an immersed plate-and-frame type filtration membrane for wastewater treatment, which comprises a plate-like support made of non-woven fabric and an organic filtration membrane formed on the surface of the plate-like non-woven fabric support. Said organic filtration membrane is an ultrafiltration membrane or a precision filtration film.
There are many types of membrane applied in the solid/liquid separation membrane biological technique; however, the pore sizes of the membranes are in the ranges of the UF and MF membranes, which limits said technique to be widely used, because of, for examples, a higher influent quality required, higher initial capital cost and energy consumption cost compared to the conventional activated sludge technique. Consequently, said technique will be more widely used, if the drawbacks can be avoided.
A primary objective of the present invention is to provide a membrane bioreactor having a non-woven fabric filtration membrane, which has a lower transmembrane pressure, a less tendency of fouling and a less energy consumption than the current solid/liquid separation membrane bioreactors.
In order to achieve the abovementioned objective, a membrane bioreactor (MBR) constructed according to the present invention comprises:
a tank containing a mixed liquor;
a filtration module immersed in said mixed liquor and having a permeate side in fluid communication with said mixed liquor only through said filtration module;
a negative pressure source for generating a hydraulic pressure on said permeate side smaller than that of the mixed liquor;
characterized in that said filtration module comprises:
a porous support having a first surface and a second surface opposite to said first surface, said porous support having pores larger than 300 xcexcm; and a non-woven fabric membrane covering said second surface, said non-woven fabric membrane having a thickness between 0.1-2 mm and pores of 0.2-100 xcexcm;
wherein said non-woven fabric membrane contacts with said mixed liquor, and the first surface of said porous support forms said permeate side.
Preferably, the shortest distance between the first surface and the second surface of said porous support is 3-10 mm.
Preferably, the bioreactor of the present invention further comprises an additional non-woven fabric membrane covering said non-woven fabric membrane. Said additional non-woven fabric membrane has a thickness of 0.1.-2 mm and pores of 0.2-100 xcexcm .
Preferably, said porous support is made of a non-woven or other porous material.
Preferably, said non-woven fabric membrane is made of a polymer material selected from the group consisting of polypropylene, polyethylene, polyamide, polyester, polyfluorocarbon, polyacrylonitrile, and polyurethane.
Preferably, said non-woven fabric membrane is hydrophilic, and is subjected to an activated grafting surface treatment of a hydrophilic monomer.
Preferably, said filtration module has a total filtration resistance of 1011-1012 mxe2x88x921 towards water.